The present invention relates to a fuel injection pump for a diesel engine and more particularly to a fuel cutoff apparatus for such a fuel injection pump which stops delivery of fuel when the pump stops.
Conventionally, a fuel distribution-type fuel injection pump used for a diesel engine propels fuel from an inlet to a pump chamber by the force of a vane pump. The rotational and reciprocal operation of a plunger cooperating with the vane pump draws fuel in the pump chamber through an intake passageway into a high-pressure chamber. Fuel is forced out of the high-pressure chamber by the plunger via a passageway provided in the plunger, a plurality of distribution holes in a housing around the plunger, corresponding discharge passageways and delivery valves to corresponding fuel injector nozzles.
The pump is provided with an electromagnetic fuel cutoff valve midway along the fuel intake passageway, which interrupts the flow of fuel to the respective injector nozzles during engine deceleration. The fuel cut-off valve is designed to re-open during engine deceleration at an engine speed greater than that at which the throttle valve opens in order to prevent abrupt changes in acceleration.
When the fuel cutoff valve is closed, it is subjected to the combination of the internal pressure of up to 10 kg/cm.sup.2 within the intake passageway and the vacuum pressure (-1 kg/cm.sup.2) from the high-pressure chamber. Thus, when the fuel cutoff valve is to be opened again, a very large force is required.
The present invention intends to facilitate actuation of the valve member in its stroke away from the fuel passageway.